1. Field of the Invention
This invention relates to a dielectric ceramic composition for low temperature sintering and, more particularly, to a dielectric ceramic composition for low temperature sintering for use as the ceramic material of a capacitor in an LC composite chip element.
2. Description of the Prior Art
Up to now, an LC composite element is comprised of an inductor and a capacitor which were separately manufactured, and widely used as a filter for example. However, it is difficult for the conventional LC composite element to cope with miniaturization of electronic parts, and manufacturing the LC composite elements as one-chip parts requires complicated processes and increases the manufacturing cost.
Therefore, there is an idea that LC components are formed by integrally molding and firing an inductance material and a capacitance material. In order to manufacture the part of the capacitor of such an LC composite element, a dielectric ceramic composition for low temperature sintering which is capable of being fired at a temperature below 1000.degree. C. and using a low cost material for internal electrodes has been required.
Until now, there have been some dielectric ceramic materials for low temperature sintering such as a BaTiO.sub.3 material including glass components of oxides of boron, bismuth and lead, and a Pb system complex perovskite material. Further, as a dielectric material for the LC composite chip element of the co-firing type, there have been a TiO.sub.2 --CuO--MnO series material disclosed in Japanese Patent Publication No. 57042/1987 and a TiO.sub.2 --CuO--NiO--MnO series material disclosed in Japanese Patent Provisional Publication No. 106120/1985.
The BaTiO.sub.3 material including glass components is not capable of being sintered at a low temperature below 1000.degree. C. while keeping the BaTiO.sub.3 's property unchanged.
The Pb system complex perovskite material is capable of being sintered at a low temperature below 1000.degree. C. and has a large dielectric constant of 10000-20000. Such a material has been disclosed in, for example, Japanese Patent Provisional Publication No. 128408/1986 and No. 128409/1986 and has a too large dielectric constant. Therefore, in order to obtain a capacity of 0.1-10 nF, it is required to enlarge the spacing between the internal electrodes or to reduce the area of the internal electrode. However, the enlargement of the spacing between the internal electrodes disables the parts from their miniaturization and the reduction of the internal electrode area causes difficulty in keeping capacity accuracy in view of parts manufacturing. Further, the linear shrinkage curve of the magnetic substance and that of the dielectric material during firing did not conform each other, and therefore cracks or warps would arise in the material during the co-firing and thus co-firing was a difficult problem to solve.
The TiO.sub.2 --CuO--MnO series material or TiO.sub.2 --CuO--NiO--MnO series material is capable of being sintered at a low temperature below 900.degree. C., but these materials have a small dielectric constant and thus could not be used for miniaturization of the part of the capacitor of an LC composite chip element and the range of capacitances obtained was narrow.